Terminal switch with thermostatic safety release



July 6, 1948. D. w. soFlELD TERMINAL SWITCH WITH THERMOSTATIC SAFETY RELEASE Filed may 5. 1945` Patented July 6, 1948 2.44am s TERMINAL SWITCH WITH THERMOSTATI SAFETY RELEASE Donald Wentworth Scofield, Detroit, Mich., as-

signor to Electromacter, Inc., Detroit, Mich., a

corporation of Michigan N Application May 5, 1945, Serial No. 592,246

Claims. (Cl. 20o-136.5)

This invention relates to an electrical appliance and more particularly to a. thermally controlled electrical connector especially adapted for use with a heating element.

An object of this invention is to provide an improved thermally controlled switching device adapted to automatically break the circuit when a predetermined temperature is reached in apparatus associated therewith.

.Another object of this invention is to provide an improved electrical .connector and switching device for use with an electrically heated device, such, for example, as a teakettle, etc.

Another object of the invention is to provide a safety electrical connector for use with a device in which liquid is being electrically heated and which will automatcally switch off the cur' rent when the lquid in the device has been ev'aporated so that the device will not be damaged by excessive heat.

A still further object of the invention is to prowardly and still showing the switch in its closed vide an improved electrical plug connector which includes in a very simple form an automatic thermally controlled electrical switch.

In accordance with the general features of this invention, there is provided in a thermally controlled electrical connector adapted for use with a heating element and as a safety device, a first housing member for connection to a heating element and a second housing member including a connector :for connection to an electrical circuit, the connector including electrical terminal means ."ournalled in the second housing member vand spring means for rotating the terminal means, said first housing member having associated with it thermally responsive means normally cooperating with the terminal means to hold the same against rotation so that said terminal means is maintained in electrical cooperation with contact means in the first housing member; the thermally responsive means upon being subjected to a predetermined temperature releasing the terminal means for rotation by the spring means to disconnectthe terminal means from the contact means and thus to-break the circuit for the heating element.

A further feature of the invention relates to the novel construction of the rotatable terminal or plug means of the connector.

Still another feature of the invention relates to the simplicity of the aforesaid structure which facilitates its application to an electrical heating appliance, such as a teakettle.

Other objects and features of this invention I will more fully appear from the following detailed position;

Figure 4 is a cross sectional view taken on the line IV-IV of Figure 2 looking in the direction indicated by the arrows and showing by dotted circles the positions to which the plug terminals are moved when the switch is open.

Figure 5 is a fragmentary sectional view taken on the line V-V of Figure 2 looking in the direction indicated by the arrows, and showing how the free extremity of the bmetallic element latchingly cooperates with the rotary terminal or plug means; and

Figure 6 is a fragmentary detailed sectional view taken on the line VI-V'I of Figure 4 looking in the direction indicated by the 'arrows and showing the construction of one of the contacts to which one end of the electrical heating element is fastened. y

As shown on the drawing:

The combination electrical connector and switch of my invention is designated generally by the reference charatcer I0 (Figure l), and is illustrated as being used in conjunction with an electrically heated appliance in the form of a teakettle, designated generally by the reference character li, which includes .a metallic vessel I2 having positioned in the bottom thereof an electrical heating element I3, which is to be connected to an electrical circuit through the connector Ill.

While I have illustrated this invention as being applied to a teakeztle in which water is to be heated, it is, of course, to be understood that my invention may be used with equaiadvantage in connection with other electrial appliances, and particularly those in which liquid is being heated and where a safety device is desired. In such *electrical appliances when the liquid evaporates or the vessel boils dry, there should be provided some automatic device for turning off the power supply so as to prevent overheating and damage to the appliance. My present connector has been developed to meet this requirement.

'I'he connector I0 embraces two housing members I4 and I5, one of which is inside of the vessel II and the other of which is on the exterior thereof. These two housing'members may comprise suitable metallic castings. For illustration, the member I4 may comprise a bronze forging or casting, whereas the member I5 may comprise a zinc or an aluminum alloy die casting. Each of them is of a hollow construction and is secured to the wall I2 of the vessel II about an opening II therein by means of four screws I8 (Figures 4 and 5). Suitable water resistant or fibre gaskets I8 and 20 are -positioned between the flanges of these members I4 and I5 and the wall I2; one gasket being on the inner side of the wall and the other on the outer. In addition, between the gasket 20 and the cooperating end of the housing member I5, there is disposed a metallic thrust plate or ring 2i which may be made of hard brass or the like. The purpose of this plate will become more apparent hereinafter.

Positioned and journaled within the housing member I5 is a rotary switch member designated generally by the reference character 22 and which carries spaced metallic prongs 23 for attachment in the usual way to a socket or the like, from which a source of electrical current is to be supplied to the heating element I3 of the electrical appliance. I preferably make the prongs 23-23 of metal, such as brass.

The rotary switch element 22 is of a spoollike construction and comprises two spaced discs 24 and 25, which may be made of brass or stainless steel. Positioned between these plates 24 and 25 is a porcelain insulator 25 which may be said to define the hub of the spool, and about which is disposed a coiled spring 21 made of spring steel wire. One end of the spring as shown in Figure 3 is anchored in a hole at 28 to the housing member I5; the other end of the spring, as shown in Figures 2 and 3, is anchored in a hole at 29 in the porcelain member 26. This arrangement is such that rotation of the member 22 to close the switch will place the spring 21 under tension.

The peripheries of the two discs 24 and 25 are rotatably journaled in a recessed portion 30 on the interior surface of the housing member I5. The outer disc 25 is held against longitudinal displacement by a shoulder 3i in the member I5. The inner or cam disc 2,4 has its outer margin bearing against the thrust plate or ring 2i so that the disc as it rotates will not engage or wear out the gasket 28.

'I'he two discs 24 and 25 and the intermediate insulator member 26 are all bolted together on the prong terminals 23 by means of suitable lock nuts 32-33.

It should be noted that the intermediate insulator 2E has not only holes therethrough for receiving the prong terminals 23-23; but in addition, is provided with insulating ring like bosses 34 and 35 on opposite sides thereof and which extend into the holes of the two discs 24 and 25 to insulate the prongs from the metallic discs. In addition insulating washers 39-39 are used to insulate the nuts 32-33 from the metal discs 25 and 24.

The inner extremities of the prong terminals 23-23 are designated by the reference character 36--36 and are `of a somewhat reduced cross sectional shape.

ject into the interior of the inner housing mem- These extremities 36-36 pro--y 4 ber I4 for cooperation with contact means to be described hereinafter.

The inner housing member I4 has suitably secured or keyed thereto a stationary porcelain contact base 31, which is recessed on its side facing the hole I3 and it is into this recess 38 that the prong extremities 33-34 Project.

Positioned in the recess are a, pair of oppositely facing goose-neck like contact blades 48-48 (Figure 4), which may be made of suitable resilient material, such, for example, as Phosphor bronze strip. These stationary contacts are engaged by the reduced extremities 38 of the prongs 23-23 when the switch is in closed position, as shown in both houses in Figure 4. When the switch is in open position the extremities 38-36 of the prongs are out of engagement with the xed contact blades 40, as shown by the dotted circles in Figure 4.

As shown in Figures 4 and 6 each of the plates 40 is secured in place by the square head of a ferrule 42 anchored by spinning to the porcelain base 31. This ferrule is threaded to receive a screw 4I for attaching an end of the heating element I3 thereto.

I'he ends of the heating element I3 project through suitable apertures into the rear of the hollow housing member I4, as shown in Figure 3, and the copper sheath which encompasses the heating or resistor element is suitably brazed at 43 to the housing member I4.

The ends 44 of the resistance wire in the heating element I3 are exposed on the interior of the housing member I4 and are extended through suitable apertures in the porcelain base 31 so that they are secured by the screws 4I to the fixed contact blades I4I), thus establishing an electrical connection between the ends of the heating element I3 and the two stationary contact blades 48-40. f

The means for controlling the operation of the switch comprises a bimetallic element or 2'strip 45 which, as shown in Figure 2, has one end secured to the inner side of the rear portion of the housing member I4 by means of screws 46. This bimetallic element is of an angular construction and has one leg projecting from the screws 46 through an aperture 41 in the porcelain base 31 so that its free end can cooperate with latching means in the form of a tang or lug 48 punched from the cam disc 24 of the rotary member 22.

Now it will be appreciated that when the member 22 is turned to close the switch by bringing the prong ends 36-36 into engagementwith the spring xed blades 40-40, the spring 21 is placed under tension and is so held by the latching of the lug or tang 48 against the free end of the bimetallic strip 45 (Figure 5).

The switch will be held in this position until such time as the bimetallic element is subjected to a predetermined temperature which results in a exure of the outer end of the bimetallic element out of the path of the cam lug 48 thereby enabling stored up energy in the spring 31 to rotate the prongs clockwise to the dotted positions shown in Figure 4 and out of engagement with the blades 40--40 thus breaking the circuit to the heating element I3.

When this combination switch and connector is used in conjunction with a teakettle, for example, the free end of the bimetallic element will move upward when the temperature in the vessel reaches some point above 212 F. This condition may arise when the liquid in the container has evaporated or has been boiled dry, in which The total amount of movement of the rotary member 22 in being moved from closed or open positions is approximately 45, and during this entire movement the discs 24 and 25 actas bearings for the rotating mechanism.

All of the parts of this combination connector and switch may be economically manufactured on a large production basis, and can be readily assembled and applied to the vessel or appliance which is to be protected.

I claim as my invention:`

1. In a thermally controlled electrical connector, a iirst housing member and a second housing member which comprises a connector ior connection to an electrical circuit and includes rotary electrical terminal means therein, as well as spring means for rotating said terminal means,

thermally responsive means associated with said iirst member and normally cooperating with said terminal means to hold same against rotation and contact means in said ilrst member engageable by said terminal means, said thermally responsive means upon being subjected to a predetermined temperature releasing said terminal means for rotation by said spring means to disconnect said terminal means from said contact means.

2. The electrical connector of claim 1 further characterized by the terminal means including a cam disc for latching cooperation with the thermally responsive means.

3. The connector of claim 1 further characterized by the thermally responsive means comprislng an angular bimetallic element having an extremity normally projecting into latching cooperation with said rotary terminal means.

4. The connector of claim 1 further characterized by the rotary terminal means comprising a spool-like assembly including spaced metallic discs having their iianges journaled in said second housing member and a hub of insulating material between said discs and about which said spring means is disposed between the same and the cooperating housing member.

5. The .connector of claim 1 further characterized by the rotary terminal means comprising a spool-like assembly including spaced metallic discs having their flanges journaled in said second mentioned housing member and a hub of insulating material between said discs and about which said spring means is disposed between the same and the cooperating housing member, one of said discs having, a tang punched therefrom for latching cooperation with said thermally responsive means.

6. The connector of claim 1 further characterizedl by said rotary terminal means including a disc journaled in the second mentioned housing member and-having formed thereon a latching tang and said thermally responsive means comprising a strip of bimetallic material disposed in said iirst mentioned housing member and having a free extremity in latching cooperv ation with said tang.

7. The connector of claim A1 4further characterized by said contacting means comprising a pairof oppositely facing spring clips mounted in said iirst mentioned housing member and by said terminal means including a pair of prongs projecting into the interior of the rst mentioned housing memfber and in engagement with said clip means, but movable out of engagement therewith upon rotation of said terminal means by said spring means.

8. In a thermal plug switch includinga housing having prongs for insertion in a socket, a rotary member in said housing to which saidprongs are connected for rotation therewith, electrical contact means in said housing for connection to said prongs, means for holding said member against rotation with said prongs electrically connected to said contact means, thermally responsive means for releasing said holding means and means for rotating said member to disconnect said prongs from said contact means.

9. In a thermal plug switch including a housing having prongs for insertion in a socket, a rotary member in said housing to which said prongs are connected for rotation therewith, electrical contact means in said housing for connection to said prongs, means for holding said mem- -ber against rotation with said prongs electrically connected to said contact means, thermally responsive means ior releasing said holding means and means for rotating said member to disconnect said prongs from said contact means, said thermally responsive means comprising a bimetallic element mounted in said housing and having a free end in latching cooperation with said rotary member but deectible out of engagement therewith upon being subjected to a predetermined temperature.

10. In a thermal plug switch including a housing having prongs for insertion in a socket, a rotary memlber in said housing to which said prongs are connected for rotation therewith, electrical contact means in said housing for connection to said prongs, means for holding said member against rotation with said prongs electrically connected to said contact means, thermally responsiye means for releasing said holding means and means for rotating said member to disconnect said prongs from said con-tact means, said rotary member -includin-g a disc iournaled in said housing member and having projecting therefrom a latchi'ng lug for cooperation with said thermally responsive means.

DONALD WENTWORTH SCOFIELD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

